1. Field of the Invention
The present invention relates to an optical disc apparatus, and more specifically, to a method for using an optical disc apparatus to accurately record data onto an optical disc in multiple write sessions.
2. Description of the Prior Art
When writing data to an optical disc, a writing session can be interrupted for many reasons. For example, one common cause is due to buffer under run, in which a buffer that stores data to be written prematurely runs out of data during a write session. While interruptions during a writing session cannot be avoided completely, in U.S. Pat. No. 6,198,707 entitled “Optical disc apparatus capable of multiple write sessions in a single track”, Yamamoto discloses a prior art optical device for handling write interruptions, which is included herein by reference. The prior art device is able to perform multiple write sessions on a single track of an optical device, thereby reducing problems associated with a write interruption.
Please refer to FIG. 1. FIG. 1 is a diagram of an optical disc apparatus 10 according to the prior art. A pickup 14 reads data from and writes data to an optical disc 12. When reading, read data is sent from the pickup 14 to a read path circuit 16, which handles read operations of the optical disc apparatus 10. The read path circuit 16 then sends data to an interface and buffer 18, which allows the optical disc apparatus 10 to communicate with a host computer and to hold data in a buffer. When writing, data to be written is taken from the interface and buffer 18 and sent to a write path circuit 19, which handles write operations of the optical disc apparatus 10. The write path circuit 19 then sends data to the pickup 14 for writing the data onto the optical disc 12.
Suppose that the optical disc apparatus 10 is interrupted during a write operation. First data was written to the optical disc 12 during the first write operation. Since the first data does not contain all desired data, which is data that was intended to be written onto the optical disc 12, the optical disc 12 will be ruined if the remaining portion of the desired data is not later written onto the optical disc 12. To handle this situation, the prior art teaches a method of writing second data onto the optical disc 12 in a separate write session. With the prior art method, second data is written onto the same track that the first data was terminated on.
Please refer to FIG. 2. FIG. 2 is a flowchart illustrating writing multiple sessions to a single track of an optical disc according to the prior art. Steps contained in the flowchart will be explained below.
Step 100: Start;
Step 102: Write first data onto the optical disc 12;
Step 104: Search for an ending location of the first data;
Step 106:
Begin writing second data in a new write session onto the same track on which the first data was terminated. The second data is written beginning at a starting location which is a fixed distance from the ending location of the first data; and
Step 108: End.
In summary, the starting location of the second data is always a same fixed distance from the ending location of the first data. Unfortunately, propagation delay in the read path circuit 16, the interface and buffer 18, and the write path circuit 19 make it difficult to precisely calibrate the optical disc apparatus 10 such that the starting location of the second data is immediately after the ending location of the first data.
Counters can be used to count sub-channel information such as the Q-code present in each sector of the optical disc 12. Furthermore, an eight to fourteen modulation (EFM) clock can be used to count sectors in the optical disc 12, and to help determine starting and ending locations of data written to the optical disc 12. Therefore, when the second data is written a fixed distance after the ending location of the first data, it is equivalent to saying that the second data is written a fixed time (as counted by clock signals) after the ending location of the first data.
Please refer to FIG. 3. FIG. 3 is a timing diagram showing a delay gap between first data and second data written to the optical disc 12 using the prior art optical disc apparatus 10. Desired data that is to be written to the optical disc 12 during a write operation is shown at the top of FIG. 3. For convenience, only a section of desired data from time=0 to time=13 is shown. Next, first data is shown starting at time=0 until a write interruption which occurs at time=6.
After the first data has been written, the prior art method includes searching for the ending location of the first data, and writing the second data starting at a fixed distance from the ending location of the first data. This entails using the pickup 14 to read the first data from the optical disc 12, and sending the first data through the read path circuit 16 to the interface and buffer 18. Once the ending location of the first data is detected, the second data (which is the remaining part of the desired data that was not included in the first data) to be written is sent through the write path circuit 19 to the pickup 14 and is then written onto the optical disc 12. Unfortunately, it is very difficult to accurately place the starting location of the second data immediately following the ending location of the first data. Therefore, as shown in FIG. 3, the beginning location of the second data is equal to a fixed time FT after the ending location of the first data. Thus, instead of the beginning location of the second data being located at time=6, the beginning location is actually at time=8 due to the fixed time FT delay. Note that the value of the fixed time FT associated with optical disc apparatus 10 may have a positive value or a negative value.
The example shown in FIG. 3 illustrates a case in which the fixed time FT has a positive value. Unfortunately, if the positive value is too large, the first and second data will have a large separation between them. This can cause synchronization to be lost between the first and second data, and all second data will be lost when later read by the optical disc apparatus 10. On the other hand, if the fixed time FT has a negative value, the beginning portion of the second data will overwrite the last part of the first data, thereby losing part of the desired data. Furthermore, since the optical disc apparatus 10 always uses the same fixed time FT to separate multiple write sessions written on a single track, an incorrect value of the fixed time FT will cause problems throughout the life of the optical disc apparatus 10.